Reliable verification of the availability of a server is of great significance in particular in the case of loosely connected client-server relations in packet-oriented data networks. If a client detects early enough that a server is overloaded or down, then it is possible to implement countermeasures in good time, such as, for example, the search for an alternative server or the creation of warning notices. Methods for verifying the availability of a server are applied, which methods also include keepalive tests described in the H.323 standard, as on 11/2000, chapter 7.2.2, if there is no permanent communication relationship between client and server and if, however, such a relationship must exist and be without fault is the basis for a desired functionality, for example, Internet telephony. In packet-oriented networks keepalive tests are used, for example, to simulate to the communication subscribers a quasi line-switching character with respect to mutual availability.
With conventional keepalive tests, a client sends availability requests to a selected server in cyclical intervals of time. If the server transmits a response to the availability request within a predefinable period of time, the server is deemed available and thus the communication relationship active. Of disadvantage in this approach is that the server is generally put under a severe load by transmitting a response to all the client requests.